1. Field of the Invention
This invention relates to a vehicle automatic transmission control system, and more particularly to a vehicle automatic transmission control system which applies fuzzy logic in such a way as to allow a multi-step or continuously variable transmission to respond and to be controlled in a manner resembling response and control based on the judgments and operations of an expert driver in the case of a conventional manually controlled vehicle transmission and which thus provides response and control that is well matched to human feelings.
2. Description of the Prior Art
In a conventional automatic transmission the time for changing gears is determined on the basis of the vehicle speed and the degree of throttle opening. More often than not the control system for carrying out this control employs a microcomputer. While control by microcomputer is superior to that by human operation in terms of speed and the volume of information that can be handled, it is often inferior to that of an expert driver in terms of quality, and for this reason has not been fully satisfactory. This is because when driving a vehicle with a manual transmission the driver does not decide to shift gears based solely on the vehicle speed and the degree of throttle opening but also takes into consideration a wide range of surrounding circumstances including the inclination of the road surface and the like. The driver then makes his decision as to whether or not to shift gears on the basis of various rules he has learned through his driving experience. For example, when driving up hill the driver decides when to shift gears taking into consideration the amount of reserve engine power available, and the more experienced he is, the more capable he will be of selecting the best gear to shift to. In the conventional automatic transmission, on the other hand, since the control or a response is based solely on the vehicle speed and the degree of throttle opening, gear changing tends to be carried out unnecessarily and repeatedly during hill-climbing, which degrades the riding comfort. Moreover, as the driving conditions change, such as when entering an uphill or downhill driving situation, the conventional automatic transmission control does no give sufficient attention to quality factors such as riding comfort, safety and fuel efficiency, which are considered important in evaluating driving performance. This has become an increasingly important problem in recent years since people no longer consider vehicles to be mere means of transportation for getting them from one place to another but want a vehicle that provides operability and performance characteristics matched to human sensibilities. There is thus a strong desire for the qualitative improvements that conventional control systems are unable to provide, and on which conventional automatic transmission control systems have been less than satisfactory.
When observing the human decision making process, it is found that a parson first acquires a general grasp of a situation, then makes a decision and acts. This process, which involves recognition, judgment, decision and action, enables the person to act or respond in a highly suitable manner notwithstanding that his or her grasp of the situation is general and imprecise.
Over the past few years, fuzzy control has come into the spotlight as a control method capable of simulating the imprecise behavior pattern of human beings. One application of such control is seen, for example, in Japanese Laid-open Patent Publication No. 63(1968)-246546 which was filed in the United States and is now matured to Patent under the number of U.S. Pat. No. 4,841,815, relating to an automatic transmission control system using fuzzy control.
Fuzzy reasoning falls into two categories including one based on fuzzy production rules and one based on fuzzy relationships. The control system disclosed in the above-mentioned publication uses reasoning by fuzzy relationships for deciding an appropriate gear ratio.
Reasoning by fuzzy relationships deals with a model expressed as complex relationships involving various fuzzy relationships connected in series and parallel. This form of reasoning is suitable for troubleshooting and other types of backward reasoning but is not appropriate for foreword reasoning which requires control values to be determined through the analysis of current phenomena. In contrast, fuzzy reasoning by rules uses a model expressed on the control side in terms of "If . . . , then . . . ," permitting the aforesaid human behavior pattern to be easily expressed and the creation of a knowledge base to be facilitated. As this mode of reasoning also makes it possible to formulate rules in the manner of a dialogue, it enables the control know-how acquired through the experience of an expert driver to be incorporated with increased accuracy so that control and response matched to human feelings can be more readily realized. Moreover, modifications in the control are easy to implement.
It was because of these advantages that the applicant proposed an automatic transmission control system based on production rules in Japanese Laid-open Patent Publication No. 2(1990)-85563 which was filed in the United States and is now being allowed. However, since the rules in this earlier system are uni-dimensionally enumerated, the number of rules is large and there remains room for improvement, particularly through modifications on the control side and other measures for increasing system simplicity.